This invention is directed to a thyristor inverter and in particular to a DC-side commutated inverter.
Presently, there are many different commutation circuits used in thyristor choppers and inverters. One of the most commonly used circuits is the McMurray inverter described in U.S. Pat. No. 3,207,974 which issued on Sept. 21, 1965 to W. McMurray. This inverter is distinguished by a high efficiency, a small number of components, a high power/weight ratio and short clearing times. However, this type of inverter requires one commutation circuit for each phase, is very sensitive to switching noise and has to rely on fuse protection in case of a shoot-through. In an attempt to conceptually simplify inverter structures a new class of DC-side commutated inverters has been developed over the past ten years. This inverter class is characterized by a single commutation circuit connected across a DC (i.e. input) bus, which, in most cases, initiates the commutation by diverting the load current away from the inverter and into the commutation circuit.
A refined version of this concept is described in the publication--"Current Source Double DC-Side Forced Commutated Inverter," IEEE Transactions Industry Applications, Vol. 1A-14, no. 6, November/December 1978, pp 581-593, by S. Martinez and F. Aldana. This inverter consists of a basic McMurray circuit together with current limiting inductances across a DC bus to obtain an input commutated inverter. Thus, at every commutation cycle, all inverter thyristors are turned off, allowing a greater flexibility in programming the output voltage waveforms. However, the type of inverter still has shoot-through problems and requires a large number of thyristors and diodes.